The so-called Precocene-1 (P1) and Precocene-2 (P2) are known substances isolated from natural sources. Bowers et al reported on the biological effects of P1 and P2 [W. S. Bowers, T. Ohta et al: Science 193, 542 (1976)]. On the basis of this biological activity it could be expected that P1 and P2 would be useful as new-type pesticide causing no environmental pollution.
Several articles have been published on the biological activity, mechanism of action and metabolism of precocenes. It is known that these compounds exert their action by damaging the juvenile hormone producing organ of insects, i.e. by special injury of the so-called "corpora allata". On testing the effects of the substances isolated from nature the correlation between the given biological group of effects and the 2H-chromene ring-system has been studied. According to experimental results the character and strength of the activity of precocenes depends to a large extent on the pest species, the test method used and from the point of view of chemical structure probably on the number and position of the substituents of the aromatic ring, the strength of the double bond of the pyrane ring and on the electronic and steric parameters of the complete molecule; [W. S. Bowers, R. Paro Martinez: Science 197 1369 (1977); H. Schoooneveld: Experientia 35 363 (1979); W. S. Bowers: Pontif. Acad. Sci. Scr. Varia 41 129 (1976); G. T. Brooks et al: Nature 281 570 (1979); T. Ohta: Kagaku to Seibutsu 17(2) 92 (1979); T. Ohta: Konchu no Seiri to Kagaku 63 (1979); G. Matolcsy et al: Z. Naturforsch. 35b. 1449 (1980); G. T. Brooks et al: Proc. Br. Crop. Prot. Conf. Pests. Dis. 1 273 (1979); G. E. Pratt et al: Nature 284 320 (1980; D. M. Soderlund et al: J. Agr. Food Chem. 28)4) 724 (1980) D. A. Schooley et al: Pestic. Biochem. Physiol. 13(2) 95 (1980); A. P. Ottridge et al: Pestic Sci. 12(3) 245 (1981). Sci. Papers of the Inst. of Org. and Phys. Chem. of Wroclaw Techn. Univ. No. 22(7) 309-424 (1981); G. E. Pratt; G. T. Brooks ed. Juvenile Hormon Biochemistry. Elsevier/North-Holland Biomed Press 311-437 (1981)].
As a result of the above research work derivatives considerably more active than natural P1 and P2 were prepared, e.g. 6-methoxy-7-ethoxy-2,2-dimethyl-2H-chromene (P3, ZR 3623) and 6-methoxy-7-isopropoxy-2,2-dimethyl-chromene.
According to prior art [CHROMANES, CHROMANONES AND CHROMONES G. P. Ellis Ed.,: John Wiley and Sons, London, pages 43-66, (1977)] 2H-chromenes can be prepared by several synthesis routes relatively independent from each other and generally these methods are used for the preparation of synthetic precocenes.
According to patent literature the corresponding analogues are obtained by similar methods (German Federal Republic Pat. No. 2,639,671, U.S. Pat. No. 4,162,326, Japanese Pat. Nos. 73121/79, 15411/80, 40637/80 and 43039/80, Spanish Pat. Nos. 496,301 and 496,302).
However the number of precocene analogues disclosed in available patent literature is rather low.